This invention relates to apparatus for testing the operation of a digital speech interpolator (DSI) for use in a time division multiple access (TDMA) scheme.
DSI is used for speech lines requiring a relatively expensive transmission path, for example, a satellite communication or the like. DSI efficiently utilizes transmission lines by transmitting speech signals during only the speech activity time. Accordingly the number of transmission lines which DSI requires is about half the number speech lines. Regarding details of DSI, reference should be made to U.S. Pat. No. 4,002,841. Since the transmission lines are expensive, the DSI must be used as efficiently and effectively as possible; therefore DSI is required to have flexibility in establishing transmission lines and to avoid trouble or fault time.
When checking or testing whether the DSI is operating normally or not due to fault, especially, when checking whether the line connection establishment (determining which channel of TDMA should be used to interconnect speech lines) is correct or not, it has been the prior art practice to actually pass a speech signal through each channel. With such a method of checking, however, a long time is necessary for the check, and that automatic checking is difficult.